<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 消除浏览器的影响 */
        *{
            margin: 0;
            padding: 0;
        }
        div{
            width: 300px;
            height: 200px;
           /* margin-top: 50px; */
           /* margin-bottom: 50px;
           margin-left: 50px;
           margin-right: 50px; */
           margin: auto;
           margin-bottom: 10px;
          background-color: red;
        }
    </style>
</head>
<body>
    <div></div>
    <div></div>
    <div></div>

    
</body>
</html>